Search

The Pelton turbine is an ideal choice for developing high-head hydropower resources. However, its cantilever-beam structure exposes the runner to intense alternating loads from high-velocity jets, causing localized high stresses, structural vibrations, and potential bucket fractures, all of which compromise safe operation. This study employs fluid–structure interaction analysis for the numerical investigation of a six-nozzle Pelton turbine to examine its unstable flow characteristics and hydrodynamic excitation under high-velocity jets. Our findings indicate that low-order frequencies primarily induce overall runner oscillations, while high-order frequencies result in oscillation, torsional displacement, and localized vibrations. Torsional displacement at the free end of the bucket induces stress concentrations at the root of the bucket and the splitter, the outflow edge, and the cut-out. The amplitudes of stress and displacement are correlated with the nozzle opening, with displacement typically in phase with torque, while stress fluctuations exhibit a phase lag. The stress and displacement values are higher on the bucket's front, with maximum stress occurring at the bucket root and maximum displacement at the outflow edge, particularly in regions subjected to prolonged jet impact. The dominant frequency of the stress pulsations matches the number of nozzles. This study elucidates the dynamic response of Pelton turbines under high-velocity jets, correlating fluid load with runner dynamics, identifying maximum stress and deformation points, and providing technical support for performance evaluation. [ABSTRACT FROM AUTHOR]

Abstract With the development of fluid-power transmission and control technology, electro-hydraulic-driven technology can significantly improve the load-carrying capacity, stiffness, and control accuracy of stabilization platforms. However, compared with mechanically driven platforms, the stiffness and damping of the fluid, as well as the coupling effect between the fluid and the structure need to be considered for electro-hydraulic-driven parallel stabilization platforms, making the modal and dynamic response characteristics of the mechanism more complex. With the aim of solving the aforementioned issues, we research the electro-hydraulic driven 3-UPS/S parallel stabilization platform considering the hinge stiffness. Moreover, the characteristic vibration equation of the mechanism is established using the virtual work principle. Subsequently, the variation characteristics of the natural frequency and the vibration response according to the position of the mechanism are analyzed based on the dynamic equation. Finally, the correctness of the model is verified by a modal test and Runge-Kutta methods. This study provides a theoretical basis for the dynamic design of electrohydraulic-driven parallel mechanisms.

Abstract Conventional light diffusers have periodic surface profiles, periodic refractive index distributions, or light scattering layers containing colloids. In all such structures the optical directivity of the light diffuser is cannot typically be controlled. Here we propose an electrically tunable light diffuser based on the application of ultrasound to a nematic liquid crystal (LC) material. The ultrasonic LC diffuser consists of an LC layer sandwiched by two glass discs and an ultrasonic transducer. The electrodes of the transducer are divided in a circumferential direction so that a resonant non-coaxial flexural vibration mode can be generated on the diffuser by controlling the electrical input signals. A continuous reversed-phase sinusoidal electric signal to the transducer generates the non-coaxial resonant flexural vibration mode on the glass disc, inducing an acoustic radiation force acting on the boundary between the LC layer and glass discs. This effect changes the molecular orientation of the LC and the transmitted light distribution. The diffusion angle of the transmitted light depends on the input voltage amplitude, and the diffusion angle was maximized at 16.0 V. The vibrational distribution and the diffusion directivity could be rotated by adjusting the input voltages to different electrodes, meaning that an ultrasonic LC diffuser with a thin structure and no moving mechanical parts provided a tunable light-diffusing functionality with rotatable directivity.

With the development of fluid-power transmission and control technology, electro-hydraulic-driven technology can significantly improve the load-carrying capacity, stiffness, and control accuracy of stabilization platforms. However, compared with mechanically driven platforms, the stiffness and damping of the fluid, as well as the coupling effect between the fluid and the structure need to be considered for electro-hydraulic-driven parallel stabilization platforms, making the modal and dynamic response characteristics of the mechanism more complex. With the aim of solving the aforementioned issues, we research the electro-hydraulic driven 3-UPS/S parallel stabilization platform considering the hinge stiffness. Moreover, the characteristic vibration equation of the mechanism is established using the virtual work principle. Subsequently, the variation characteristics of the natural frequency and the vibration response according to the position of the mechanism are analyzed based on the dynamic equation. Finally, the correctness of the model is verified by a modal test and Runge-Kutta methods. This study provides a theoretical basis for the dynamic design of electrohydraulic-driven parallel mechanisms. [ABSTRACT FROM AUTHOR]

Taking the nonlocal effect into account, the vibration governing differential equation and boundary conditions of a magnetostrictive composite cantilever resonator were established based on the Euler magnetoelastic beam theory. The frequency equation and vibration mode function of the composite cantilever were obtained by means of the separation of variables method and the analytic solution of ordinary differential equations. The lateral deflection, vibration governing equations, and boundary conditions were nondimensionalized. Furthermore, the natural frequency and modal function of the composite beam were quantitatively analyzed with different nonlocal parameters and transverse geometry dimensions using numerical examples. Compared with the results without considering the nonlocal effect, the influence of the nonlocal effect on the vibration characteristics was analyzed. The numerical results show that the frequency shift and frequency band narrowing of the magnetostrictive cantilever resonator are induced by nonlocal effects. In particular, the high-frequency vibration characteristics, such as vibration amplitude and modal node of the composite beam, are significantly affected. These analysis results can provide a reference for the functional design and optimization of magnetostrictive resonators. [ABSTRACT FROM AUTHOR]

As a complex load-bearing system, high-speed tracked vehicles not only need to have certain protective capabilities, but also need to be able to withstand the effects of various excitation sources. With the emergence of lightweight design requirements for vehicle bodies, research on the design of such high-speed tracked vehicles is gradually deepening. The modal analysis of vehicles is related to the reliability design of the vehicle bodies. However, current research on the modal characteristics of lightweight high-speed tracked vehicles is mainly based on experimental methods, which cannot conduct extensive research on the dynamic response of vehicle bodies under different application conditions. Modal calculation and analysis were conducted on the vehicle body model of a lightweight high-speed tracked vehicle based on the finite element method, and the model was modified combined the experimental modal test results. And, the suggestions were made for optimizing the design of the vehicle body. The modified vehicle body model and modal characteristics were contributed scholars to analyze the rationality of relevant vehicle structural design, thereby avoiding resonance during vehicle movement. Moreover, the research results are expected to be applied to analyze the dynamic characteristics of the vehicles under different working conditions, and provide reference and guidance for the design and modification of the lightweight highspeed tracked vehicles. [ABSTRACT FROM AUTHOR]

In this article, the design process of a novel vibrating tool is presented to improve some key aspects of Single Point Incremental Sheet Forming (SPISF). The overall effect of a vibration assistance is an improvement of the process by decreasing certain constraints occurring during manufacturing (e.g., high forming forces, poor roughness and elastic springback). For developing such assistance, the objective of this study is to present the design methodology and characterization of an innovative tool. The horn-shape design of the tool is optimized to resonate at its natural frequencies in the 4–16 kHz frequency bandwidth. A frequency decoupling of the tool modes is obtained by a successful desymmetrization of the tool design to precisely control the vibration direction, focusing on axial, radial or coupled vibrating motion of the tool tip. Then, the unidirectional vibrating force generated by a piezoelectric actuator is transformed into a controlled multidirectional vibrating motion of the tool tip depending on the frequency and the amplitude of the actuator input signal. The core contribution of the paper is the design methodology itself of the forming tool, which encompasses a novel approach focused on the tool/sheet contact coupling analysis and its effect on the vibrating behavior of the tool during SPIF process conditions. All steps of the design methodology are described: from the design specifications to the prototype validation, including a finite element analysis and an experimental characterization of its modal behavior in free-end tool conditions as well as in different tool/sheet contact conditions through a simple indentation forming test inside an AA5086 metal sheet. Experimental results highlight the importance of considering process boundary conditions for modal identification and the influence of the vibration direction on the force reduction in forming conditions. A forming force reduction up to 26% is obtained exciting the 2 nd bending mode of vibration of the presented forming tool identified in tool/sheet contact configuration, while reduction is less significant for the 1 st and 3 rd bending modes. [ABSTRACT FROM AUTHOR]

Aiming to address the vibration noise problems on ships, we constructed a piezoelectric phononic crystal (PC) plate structure model, solved the governing equations of the structure using the partial differential equations module (PDE) in the finite element softwareCOMSOL6.1, and obtained the corresponding energy band structure, transmission curves, and vibration modal diagrams. The application of this method to probe the structural properties of two-dimensional piezoelectric PCs is described in detail. The calculation results obtained using this method were compared with the structures obtained using the traditional plane wave expansion method (PWE) and the finite element method (FE). The results were found to be in perfect agreement, which verified the feasibility of this method. To safely and effectively adjust the bandgap within a reasonable voltage range, this paper explored the order of magnitude of the plate thickness, the influence of the voltage on the bandgap, and the dependence between them. It was found that the smaller the order of magnitude of the plate thickness, the smaller the order of magnitude of the band in which the bandgap was located. The magnitude of the driving voltage that made the bandgap change became smaller accordingly. The new idea of attaching the PC plate to the conventional plate structure to achieve a vibration damping effect is also briefly introduced. Finally, the effects of lattice constant, plate width, and thickness on the bandgap were investigated. [ABSTRACT FROM AUTHOR]

Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance. • Coupling control for flexible spacecraft. • Active vibration control using positive position feedback. • Model compensation control term is constructed to improve the dynamic performance. • The obtained closed-loop system achieves the asymptotic stability and anti-unwinding performance. [ABSTRACT FROM AUTHOR]

This study focuses on a marine two-stage tandem hybrid planetary system. Natural frequencies and vibration modes are determined using a translational–torsional coupled dynamic model. Based on the motion characteristics of the transmission system, free vibration is categorized into three typical modes. The parameter sensitivity of natural frequencies is computed, and the effects of structural parameters such as unequally spaced planet, mesh stiffness, planet mass and rotational inertia on the natural frequencies are analyzed. Utilizing the coupling factor, the mode transition criterion for the natural frequencies response to parameters is formulated. The results demonstrate that the vibration modes of the two-stage tandem hybrid planetary system can be classified as the fixed-axis train vibration mode, the differential train vibration mode, and the coupled vibration mode. Unequally spaced planet primarily disrupts vibration modes without significantly affecting natural frequencies. In contrast, the effects of mesh stiffness, planet mass and rotational inertia on the modes are opposite to those of unequally spaced planets. The validity of the parameter sensitivity and mode transition criterion is substantiated through illustrative examples. [ABSTRACT FROM AUTHOR]

Although the compressive strength is the most commonly used property to characterize mortars, it has limited representativeness in real-world applications. The deformation properties of mortars, specifically the elastic modulus, are responsible for masonry behavior. However, there is currently no standard method for determining the elastic modulus of mortars and no consensus on the best approach. Therefore, the aim of this paper is to obtain both static and dynamic moduli of a one-coat rendering mortar following the standards for calculating them on concrete specimens and verify their validity. The static modulus was determined under compression by adapting the standard for concrete specimens (EN-1352) to mortars using two gauges, and under the flexural tensile test following the standard EN-1015–11. The dynamic modulus was calculated by measuring the fundamental resonant frequencies of longitudinal and transverse vibration modes, adapting the American standard for concrete (ASTM C215) for mortar. The tests were performed on both standardized and non-standardized prismatic specimens, as well as in situ samples at various ages. The results indicated that dynamic modulus obtained from the longitudinal vibration mode was higher than that from the transverse mode, but differences were smaller using a uniaxial accelerometer than with a triaxial accelerometer. The dynamic modulus exhibited a slightly higher value and lower dispersion than the static modulus. Both moduli decreased with time and were easily correlated through linear regressions. Additionally, both moduli were correlated with flexural and compressive strength values. In situ samples had lower elastic moduli, but the compaction procedure in real works differs from laboratory tests. In summary, it was demonstrated that the procedures for calculating dynamic and static elastic moduli in concrete can be applied to mortar samples, and their effectiveness was confirmed.

Abstract As a means of vibration reduction, the ladder track has seen broad implementation in urban rail transit. However, issues such as increased vibration noise, rail corrugation, and fastener failure have been observed in certain sections of the ladder track during later operation. To investigate the mechanisms behind these phenomena and provide comprehensive insights into the system's response to various operational conditions, this study employed vehicle-track coupled dynamic theory to establish a three-dimensional finite element model of the flexible vehicle-ladder track system. The vibration transmission and dynamic response characteristics of the vehicle-ladder track system were analyzed. The findings revealed that the vehicle-track resonance and anti-resonance phenomena were more prominent in the medium- to low-frequency range. At specific frequencies, the wheelset exhibited various vibration modes, and the fastener force was found to closely correlate with the ladder vibration mode. Furthermore, the influence of speed on diverse components of the vehicle-ladder track system, in terms of maximum vibration and the dominant vibration frequency range, differed considerably. This study provides a more comprehensive and reasonable exploration of the modeling and dynamic behavior of vehicle-ladder track systems.

As a means of vibration reduction, the ladder track has seen broad implementation in urban rail transit. However, issues such as increased vibration noise, rail corrugation, and fastener failure have been observed in certain sections of the ladder track during later operation. To investigate the mechanisms behind these phenomena and provide comprehensive insights into the system's response to various operational conditions, this study employed vehicle-track coupled dynamic theory to establish a three-dimensional finite element model of the flexible vehicle-ladder track system. The vibration transmission and dynamic response characteristics of the vehicle-ladder track system were analyzed. The findings revealed that the vehicle-track resonance and anti-resonance phenomena were more prominent in the medium- to low-frequency range. At specific frequencies, the wheelset exhibited various vibration modes, and the fastener force was found to closely correlate with the ladder vibration mode. Furthermore, the influence of speed on diverse components of the vehicle-ladder track system, in terms of maximum vibration and the dominant vibration frequency range, differed considerably. This study provides a more comprehensive and reasonable exploration of the modeling and dynamic behavior of vehicle-ladder track systems. [ABSTRACT FROM AUTHOR]

Shear-type structures are common structural forms in industrial and civil buildings, such as concrete and steel frame structures. Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures. The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment. However, for many shear-type structures, it is difficult to obtain accurate FEM. In order to avoid finite element modeling, a model-free method for diagnosing shear structure defects is developed in this paper. This method only needs to measure a few low-order vibration modes of the structure. The proposed defect diagnosis method is divided into two stages. In the first stage, the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage. In the second stage, damage severity is evaluated based on an improved frequency sensitivity equation. The main innovations of this method lie in two aspects. The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure. The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite element model. This method has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure. Based on numerical analysis and experimental data validation, it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree, and does not require finite element modeling. The proposed method should be a very simple and practical defect diagnosis technique in engineering practice. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the dynamic behaviour of asphalt concrete substructure ballastless track system (ACSBTS) in the application of long-span railway bridge (LSRB) is clarified. Firstly, the finite element model of full LSRB was established, which considered the viscoelastic properties of asphalt concrete and the vibrational load condition of high-speed train. Particularly, the asphalt concrete properties were characterised using generalised Maxwell model. Then, the dynamic responses of different components in ACSBTS were calculated and compared with those of cement concrete substructure ballastless track system (CCSBTS). Moreover, the LSRB vibration modes were discussed. Lastly, the effect of different influence factors was investigated. Results show that asphalt concrete substructure can mitigate the mechanical responses induced by dynamic train load. It is suggested that the asphalt concrete substructure thickness should preferably not exceed 350 mm and its modulus could be increased appropriately. Findings contribute to the application of ACSBTS in LSRB. [ABSTRACT FROM AUTHOR]

Material damage in structures must be detected in a timely manner to prevent engineering accidents. Damage detection based on structural flexibility has attracted widespread attention in recent years due to its simplicity and practicality. This article provides a detailed overview of damage detection methods based on structural flexibility. Depending on the calculation method and data used, flexibility-based methods can be divided into the following categories: flexibility difference, flexibility derivative index, flexibility sensitivity, flexibility decomposition, static flexibility, and combinations of flexibility with other methods. The basic principles and main calculation formulas of various flexibility methods are explained, and their advantages and disadvantages are analyzed. For the method using flexibility difference, the advantage is that the calculation is very simple and does not require the construction of a finite element model of the structure. The disadvantage is that it requires the measurement of modal data of the intact structure, and this method cannot quantitatively assess the degree of damage. For the method using the flexibility derivative index, the advantage is that it only requires the modal data of the damaged structure to locate the damage, but this method is particularly sensitive to noise in the data and is prone to misjudgment. For methods based on flexibility sensitivity and flexibility decomposition, the advantage is that they can simultaneously obtain the location and degree of damage in the structure, but the disadvantage is that they require the establishment of accurate finite element models in advance. Static flexibility methods can compensate for the shortcomings of dynamic flexibility methods, but they usually affect the normal use of the structure during static testing. Combining flexibility-based methods with advanced intelligent algorithms and other methods can further improve their accuracy and efficiency in identifying structural damage. Finally, this article discusses the challenges that have not yet been solved among damage detection methods based on structural flexibility. [ABSTRACT FROM AUTHOR]

ObjectiveThis study analyzes different high-skew propeller blade parameters to obtain the laws of their influence on blade vibration modes. MethodsA certain high-skew propeller is taken as the research object, a series of variable parameter schemes is designed and the finite element calculations for the vibration modes are conducted. The numerical method is validated effectively by adopting model tests. Through an analysis of the calculation results, the influence laws of the different design parameters on the blade natural frequency, attenuation coefficient and mode shapes are obtained. ResultsThe calculation results show that the blade natural frequency increases with its sectional thickness, area ratio and hub ratio, and decreases with its skew angle. Furthermore, the sectional thickness and skew have the greatest influence among the research parameters. The fluid-structure interaction effect has the greatest influence on the first order attenuation coefficient. The increase of the sectional thickness overall or at the outside radius is beneficial for reducing the first order attenuation coefficient. On the contrary, the increase of the area ratio, inward movement of skew balance point and large rake angle design is negative for first order attenuation coefficient reduction. The first order mode shape is almost the same for the series design scheme, which means that changes of the design parameters such as sectional thickness and skew angle mainly influence the blade's high order mode shapes. ConclusionThe results of this study can provide guidance and references for vibration mode optimization control in the design process of high-skew propellers.

Taking the nonlocal effect into account, the vibration governing differential equation and boundary conditions of a magnetostrictive composite cantilever resonator were established based on the Euler magnetoelastic beam theory. The frequency equation and vibration mode function of the composite cantilever were obtained by means of the separation of variables method and the analytic solution of ordinary differential equations. The lateral deflection, vibration governing equations, and boundary conditions were nondimensionalized. Furthermore, the natural frequency and modal function of the composite beam were quantitatively analyzed with different nonlocal parameters and transverse geometry dimensions using numerical examples. Compared with the results without considering the nonlocal effect, the influence of the nonlocal effect on the vibration characteristics was analyzed. The numerical results show that the frequency shift and frequency band narrowing of the magnetostrictive cantilever resonator are induced by nonlocal effects. In particular, the high-frequency vibration characteristics, such as vibration amplitude and modal node of the composite beam, are significantly affected. These analysis results can provide a reference for the functional design and optimization of magnetostrictive resonators.

The vibration mode of the radiation surface of transducer (or structure of supersaturated cavitation cloud in thin liquid) is investigated experimentally by high-speed photography. The classification of saturated, supersaturated and undersaturated cavitation clouds was proposed, and a comparison was made between saturated and supersaturated cavitation cloud structures in liquid thin layers. The characteristics and formation mechanism of supersaturated cavitation cloud structure were investigated. Based on the close correspondence and rapid response between the distribution of supersaturated cavitation clouds and vibration modes of radiation surface, a new approach is proposed to measure the vibration mode of transducer operating at high power and large amplitude in real time.

Background: The traditional piezoelectric motors have the disadvantages of sliding friction and and low life. The non-contact piezoelectric motors can remove the friction between stator and rotor, but their output torque is relatively small. Purpose: A novel piezoelectric motor should be developed to obtain relatively large output torque and avoid sliding friction simultaneously. Dynamic characteristic is an important factor of a system performance. So, the dynamic characteristic of the proposed piezoelectric motor should be developed. Methods: The proposed piezoelectric motor consists of multi-elements among which, some could be simplified as continuum model and other could be simplified as lumped parameter model. It is a hybrid dynamics system and difficult to resolve. After introducing structure and operation principle of the motor, a hybrid dynamic model combining continuum model with lumped parameter model for the motor system is proposed. Using the hybrid dynamic model, the natural frequencies and vibration modes of the motor system are investigated. Results: The torsional vibration of the rotor and the bending vibration of the rotor in the x-axis are less restricted by the system and their amplitudes are relatively large. In the y axis, the vibration amplitudes of the whole elements are close to each other for the low order modes. For the medium-high frequencies, the axial vibration of the piezoelectric stack or the axial vibration of the piezoelectric stack plus the lateral vibrations of the beam and circular arc displacement amplifier is relatively large. Conclusion: The dynamics performance design of the motor should be focus on the torsional vibration and the x direction bending vibration of the rotor. Under medium-high excitation frequencies, the axial vibration of the piezoelectric stack and the lateral vibrations of the beam and arc displacement amplifier should be considered. [ABSTRACT FROM AUTHOR]

Compared to onshore turbines, floating offshore wind turbines (FOWTs) take advantage of the increased availability of offshore wind while causing less environmental impact. However, the strong winds, waves, and currents to which they are subjected trigger oscillations that can cause significant damage to the entire structural system and reduce its useful life. To reduce these loads, active tower damping techniques such as filter banks can be used. These filters must be carefully tuned to block specific vibration frequencies. Therefore, it is essential to analyze the nature of the oscillations in the FOWT and to understand how the frequencies vary in time. This topic is usually approached from a point of view very focused on a specific turbine. What is proposed here is a general method, which can be applied to any type of wind turbine, to automatically study the relationship between vibration frequencies and the degrees of freedom (DOF) of the turbine, which facilitates the design of structural control. Each frequency is associated with the DOF of the FOWT that produces it. This methodology has been successfully validated in simulation experiments with the NREL 5 MW ITI Barge FOWT. Under the wind conditions of the experiments, the main frequency found is 0.605 Hz. This frequency coincides with the 3P theoretical frequency of the FOWT. This proposal may help to design structural control systems able to damp these vibration frequencies with accuracy and efficiency. [ABSTRACT FROM AUTHOR]

Planetary herringbone gears are increasingly used in the high-power marine transmission system. In order to meet the noise requirements of transmission system of modern ships, the vibration reduction design of planetary herringbone gear transmission system is not only of practical value, but also of theoretical significance. Aiming at the planetary herringbone gear transmission in the power system of a ship, the analytical expression of the dynamic meshing force between the center gear and the planetary gear is established, and the coupling law between the number of teeth of planetary and center gear, the number of planetary gear and the vibration amplitude caused by the meshing frequency excitation is obtained. Based on the corresponding relationship between the vibration mode caused by time-varying meshing stiffness excitation and the natural vibration mode of the transmission system, and by reasonable design of basic parameters of planetary herringbone gear transmission, a phase tuning vibration reduction design method is proposed to suppress the torsional vibration of the system. The method has been verified to achieve the purpose of suppressing torsional resonance of the central member.

This study focuses on a marine two-stage tandem hybrid planetary system. Natural frequencies and vibration modes are determined using a translational–torsional coupled dynamic model. Based on the motion characteristics of the transmission system, free vibration is categorized into three typical modes. The parameter sensitivity of natural frequencies is computed, and the effects of structural parameters such as unequally spaced planet, mesh stiffness, planet mass and rotational inertia on the natural frequencies are analyzed. Utilizing the coupling factor, the mode transition criterion for the natural frequencies response to parameters is formulated. The results demonstrate that the vibration modes of the two-stage tandem hybrid planetary system can be classified as the fixed-axis train vibration mode, the differential train vibration mode, and the coupled vibration mode. Unequally spaced planet primarily disrupts vibration modes without significantly affecting natural frequencies. In contrast, the effects of mesh stiffness, planet mass and rotational inertia on the modes are opposite to those of unequally spaced planets. The validity of the parameter sensitivity and mode transition criterion is substantiated through illustrative examples.

With the continuous acceleration of the global construction industry, many structural infrastructure structures in China have been put into use for decades. They are very prone to damage due to fatigue. The modal parameter identification of civil engineering construction can evaluate the safety status of infrastructure structures. In view of this, an identification system of civil engineering structure modal parameters is proposed based on improved wavelet transform. In the process, the mode shape was chosen as the method of wavelet transform. The data was discretized by selecting the actual data of a high-speed railway station combined with sensors and wavelet transform. Finally, the correct identification of the modal parameters of civil engineering structures is realized. The data shows that under normal conditions where there is only white noise interference, the waveform of the structure is relatively stable, and the amplitude fluctuation is in the [-2,3] interval. At the same time, the average amplitude of the structure is in the [2.2, −1.5] interval under normal conditions. In addition, the positive and negative extreme points are 3.7 and −2.3, respectively. This indicates that the structure amplitude fluctuation is in a dynamic and stable state under normal circumstances. The optimized wavelet transform method identifies a total of four orders in the first six natural frequencies. The minimum error is 0.11%, the maximum error is 1.50%, and the average error of the first four natural frequencies is 0.578%. In addition, based on the comparison of theoretical and identification values of longitudinal vibration shapes, the proposed method can successfully detect abnormal values at the 10th and 18th nodes. From the above results, it shows that the wavelet transform method has high accuracy and small error in frequency identification. It meets the requirements of identifying the natural frequency parameters of the structure. From the calculation, the method proposed in the experiment can realize the real-time health detection of the structure, which is of great significance.

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aims: To find the prevalence of tactile hallucinations of phone vibrations among individuals aged 18 years-22 years. To find whether the hallucinations are bothersome. Background: Overuse of phones can lead to physiological health hazards. Repeated use of vibration mode leads to fake perception of device being vibrating when it is not. Tactile hallucination of phone vibration is a prevalent phenomenon among young individuals. Theories explaining the possibility of the phenomenon are proven through researchers. Design: Cross sectional survey. Participants: 204 individuals responded to the questionnaire. Materials and Methods: An electronic survey consisting of 12 questions bases on demographic, mobile usage hours, frequency of phantom vibrations experienced. An online questionnaire was used for the study. It is known as the phantom vibration scale or phantom vibration questionnaire which was taken from an article. Results: 204 responses were received. Out of that 68% experienced tactile hallucinations. Among those who had hallucination different factors were viewed in association with it. 88% possessed a smart phone for more than a year. Respondents were asked about the phone usage hours and majority used it for 3 hours-5 hours daily. Social media is a known addiction of phone and the survey showed that 55% of the respondents used phones to scroll social media. The next factor that is vibration mode of phone, was used by 17% of the people always. 29% used it for most of the time. About the placement while carrying of phone it showed that 69% always carried phone in their jean front pocket. Also, 42% of the participants found those vibrations to be bothersome. 21% had the hallucinations so severe that they felt it when the phone was switched off. Conclusions: More than half of the people on this planet carry smartphone and most use it on vibration mode. Even if one third of them experience the hallucinations, a planned treatment is required for this. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The diagnosis of structural damage usually belongs to a mathematical inverse problem. This work presents a novel frequency-shift flexibility sensitivity algorithm for structural damage assessment using only the first-order vibration mode to achieve the goal of successfully identifying structural damage with fewer modal parameters. The core idea of the proposed method is to make the first-order vibration mode contribute the most to a structural flexibility matrix through the frequency-shift operation. A high-precision flexibility matrix can be obtained after the frequency-shift operation, which only needs the first mode of structural free vibration. Through this special advantage, structural damage coefficients can be accurately calculated by the frequency-shift flexibility sensitivity equation. Thus, a reliable identification result can be obtained according to the values of the calculated damage coefficients. In some engineering applications, another advantage of the proposed method is that it does not require a complete finite element modeling process, as long as a few lower-frequency vibration modes of the intact structure are measured. A truss structure and a beam structure are used as two numerical examples to demonstrate the proposed approach. The results show that the proposed method has higher calculation accuracy than the ordinary flexibility sensitivity method by using only the first-order vibration mode. The proposed method can overcome possible misdiagnosis of the ordinary flexibility sensitivity method. It also has been shown that the proposed method may have the potential to identify minor damage in a structure. Using the experimental data of a steel frame structure, the effectiveness and reliability of the proposed method have been further verified. The proposed method provides a simple way for structural damage identification with only a few vibration modal data. [ABSTRACT FROM AUTHOR]

Dynamic mesh atomizers have been widely used in various fields because of their compact structure, low energy consumption, and low production costs. The finite element method is an important technique to analyze the factors affecting the atomization performance of dynamic mesh atomizers. However, at present, there is a lack of decisive solutions to the basic problems of boundary setting in terms of the simulation and vibration displacement characteristics of atomizers under different vibration modes. In this paper, two errors were found in the Vibration Analysis of a Piezoelectric Ultrasonic Atomizer to Control Atomization Rate paper written by Esteban Guerra-Bravo et al. in 2021. First, in the finite element analysis, the boundary condition of the atomizing sheet was set to be fixed, which is inconsistent with the actual support situation and seriously affects the vibration of the atomizing sheet. Second, in the simulation result, from the first mode to the third mode, the growth rate of the maximum displacement at the center of the atomizing sheet was as high as 77.12%, even up to 221.05%, which is inconsistent with the existing vibration theory. In view of these errors, in this paper, the working principle of dynamic mesh atomizers is analyzed and the vibration equation of the atomizing sheet under peripheral simple support is derived. Through comparison with the literature, it was proven that the boundary setting and vibration displacement of the atomizing sheet in the original paper are unreasonable. By measuring the atomizing rate of the atomizing sheet under different boundary conditions, it was proven that the peripheral freedom of the atomizing sheet should be greater than or equal to 1, namely, peripheral freedom or peripheral simply supported. The vibration displacement theory was used for the simulation, and the relationship between the vibration displacement and resonant frequency of the atomizing sheet under peripheral simple support was measured. It was found that with the increase in the resonance frequency, the maximum displacement of vibration modes with only nodal circles was larger than that of the other vibration modes, and the maximum displacement increased slightly with the increase in the number of nodal circles by about 0.98%. [ABSTRACT FROM AUTHOR]

Here, we report the distinct behaviors of 4‐azidobenzoic acid (C7H5N3O2, 4‐ABA) in diamond anvil cells with the pressure up to ∼18 GPa at room temperature by in situ Raman scattering and synchrotron angle‐dispersive X‐ray diffraction (ADXRD) measurements. The analyses of Raman spectra revealed that 4‐ABA underwent a phase transition in the pressure range of 0.8–1.3 GPa and a conformational change at 6.3 GPa, which were supported by XRD results. The phase transition is attributed to the distortion of the benzene ring, and the change of hydrogen bonds results in the conformational change. Above 11.2 GPa, the (112) Bragg peak moved toward a low angle, indicating the increase of the interplanar distance of 4‐ABA. Upon compression to 18.0 GPa, 4‐ABA transformed into amorphous phase that the low amorphization pressure is helpful for nitrogen polymerization. This study provides an effective route for understanding the evolution of the azide group under high pressure, which is beneficial to studying the mechanism of forming polymeric nitrogen. [ABSTRACT FROM AUTHOR]

In order to study the electromechanical coupling mechanism of the micro-robot joints in the unsteady working state and considering the time-varying stiffness and error of gear meshing， a lumped parameter method is adopted to establish an electromechanical coupling model of the motor-driven two-stage series planetary gear transmission system. The influence of the natural frequency， and quality parameters of the system on the natural frequency of the system and the distribution law of modal energy is calculated and the torsional vibration characteristics of the gear system under impact load are analyzed. The research results show that as the quality of parts increases， the natural frequency of the system shows a downward trend. The modal energy of the system is mainly manifested as low-order torsional vibration strain energy and high-order kinetic energy. During the impact process， the system behaves as a vibration mode dominated by a first-order natural frequency and a one-time meshing frequency.

In recent decades, various single-phase drive ultrasonic motors have emerged, and only a single excitation signal is used in their working states. Single-phase driven ultrasonic motors have the benefits of most ultrasonic motors, as well as the advantages of a simple driving circuit construction, low cost, high design flexibility, and high reliability, among others. According to the working principles, they are divided into three types: the vibration mode alternating type, the vibration mode coupling type, the vibration mode converting type. This paper summarizes various types of single-phase ultrasonic motors. The three types of the working principles and its representative structures are explained; output performances of the single-phase ultrasonic motors are described; then, practical and potential applications of the single-phase ultrasonic motors are introduced; finally, the research of single-phase ultrasonic motors are reviewed, and its development prospect is prospected. This review is helpful for a comprehensive understanding of single-phase drive ultrasonic motors. This paper offers the groundwork for the development of a novel single-phase driven ultrasonic motor with improved mechanical output. [ABSTRACT FROM AUTHOR]

Multilayer piezoelectric ceramics have wide application prospects in the fields of precision driving and intelligent sensing owing to their low driving voltages and large strains. However, high sintering temperatures and expensive noble metal electrodes limit their application as multilayer piezoelectric ceramic actuators (MLAs) in conventional devices. In this study, a modified piezoelectric ceramic powder and Ag inner electrode were used to prepare a low-cost MLA with a low sintering temperature of 900 °C. The MLA showed superior piezoelectric properties with d 33 = 3015 pC/N and a large electric-field-induced strain of 0.13% at 22.2 kV/cm. Moreover, the stator of the ultrasonic motor composed of this MLA produced the ideal vibration mode, and the maximum rotation speed of the ultrasonic motor was 192 r/min under a 50 g load, which verifies the applicability of this component in practical minimised devices. These results demonstrate a strategy for fabricating low-cost and high-precision micro-actuators for precision driving. [ABSTRACT FROM AUTHOR]

The structure of DNA double helix is stabilized by water molecules and metal counterions that form the ion-hydration shell around the macromolecule. Understanding the role of the ion-hydration shell in the physical mechanisms of the biological functioning of DNA requires detailed studies of its structure and dynamics at the atomistic level. In the present work, the study of collective vibrations of water molecules around the DNA double helix was performed within the framework of classical all-atom molecular dynamics methods. Calculating the vibrational density of states, the vibrations of water molecules in the low-frequency spectra ranged from ∼ 30 to ∼ 300 cm - 1 were analyzed for the case of different regions of the DNA double helix (minor groove, major groove, and phosphate groups). The analysis revealed significant differences in the collective vibrations behavior of water molecules in the DNA hydration shell, compared to the vibrations of bulk water. All low-frequency modes of the DNA ion-hydration shell are shifted by about 15–20 cm - 1 towards higher frequencies, which is more significant for water molecules in the minor groove region of the double helix. The interactions of water molecules with the atoms of the macromolecule induce intensity decrease of the mode of hydrogen-bond symmetrical stretching near 150 cm - 1 , leading to the disappearance of this mode in the DNA spectra. The obtained results can provide an interpretation of the experimental data for DNA low-frequency spectra and may be important for the understanding of the processes of indirect protein–nucleic recognition. [ABSTRACT FROM AUTHOR]

The vibration mode of bend pipe and the choking prevention effect in dense-phase pneumatic conveying has been investigated experimentally. The vibration mode has been showed that it has four antinodes for longitudinal direction, and eight for pipe cross section as designed, and the vibration amplitude has increased as increasing the input voltage. Therefore, it is possible to adjust the vibration amplitude easily by changing the input voltage. Then, the frictional force between the packed bed and pipe wall has been increased with increasing particle diameter. However, it has been reduced with ultrasonic vibration in spite of kinds of particles and pipe diameter. This means the possibility of choking can be removed with ultrasonic vibration in bend pipe as well as in horizontal pipe. [ABSTRACT FROM AUTHOR]

A structure can experience vibration at a certain level, parameters such as material properties, position of supports, and system frequency determine their vibration characteristics. This study aims to analyze the relationship between natural frequency and vibration mode using both Autodesk Inventor software and experimental method. Vibration mode analysis was carried out on 5 modes of a cantilevered aluminum beam. Experimental tests were also carried out to measure the dynamic responses or vertical vibration displacements using a vibration meter. The beam used was 6061 Aluminum series material with a length of 90 cm with 5 measurement points at an interval of 18 cm. The results show that each of natural frequency (wn) has a different vibration mode. The experimental results show the same trend as the simulation results. Thus, the vibration are determined by the frequencies applied to the system and measurement positions on the cantilevered aluminum beam.

Rotational acoustic manipulation technology offers precise control of particle motion, making it advantageous for applications in microfluidics, biomedicine, materials research, and so on. Current advanced techniques that use acoustic waves to rotate particles include microstructure vibration, microbubble oscillation, and acoustic holography. Although these methods have achieved some success in rotational acoustic manipulation, they face challenges such as limited types of particles, complex device fabrication, and single-mode manipulation. To address these issues, this study proposes a novel rotational acoustic manipulation device based on traveling wave acoustic fields. The traveling wave acoustic field is achieved by planning the vibration modes of the vibrational source. In this study, a ring-shaped piezoelectric ceramic with four-quadrant dual polarization is designed to excite two orthogonal B 11 bending vibration modes of the vibrator. By adjusting the phase difference of the excitation signals, these two B 11 bending vibration modes can be coupled into either clockwise or counterclockwise traveling wave vibration modes, thereby establishing unidirectional rotating traveling waves in the water within the PDMS ring. The PDMS ring features an open structure, meeting the requirements for manipulating both floating and submerged particles. The performance of the proposed acoustic manipulation device is validated and analyzed through experiments with hollow glass particles, hollow polystyrene particles, and solid polystyrene particles. The results demonstrate that the proposed acoustic manipulation device can achieve precise fixed-point self-rotation and regional revolution manipulation of particles, regardless of their floating, submerged, hydrophilic, or hydrophobic properties. This indicates the high universality and robustness of the device, making it applicable for the manipulation of various types of particles. Overall, this study introduces a novel acoustic manipulation method for particle rotation, providing strong support for the development and application of acoustic manipulation devices in diverse fields. [Display omitted] • A novel piezoelectric device is proposed for manipulating the self-rotation and revolution of particles. • The rotating acoustic field and acoustic streaming field are established in water by planning the vibration modes. • The proposed manipulation device is effective regardless of whether particles are floating or submerged. • Both hydrophilic and hydrophobic particles can undergo self-rotation and revolution within the proposed device. [ABSTRACT FROM AUTHOR]

In dynamic model of planetary gears, one of the key design parameters and one of the main sources of vibration is time–varying mesh stiffness of meshing gears. According to previous researches, the finite element method and analytical method are two techniques to estimate the mesh stiffness of meshing gears. In this work, in an innovation the periodically time–varying mesh stiffness of meshing gears is examined by both of finite element and analytical methods. The planetary gear set is modeled as a set of lumped masses and springs. Each element such as sun gear, carrier, ring gear and planets possesses three degrees of freedom and is considered as rigid body. The influence of effective parameters on the mesh stiffness of meshing gears and also numerical results of natural frequencies and vibration modes of the system are obtained. Based on the results, the influence of the higher pressure angles on the mesh stiffness of meshing gears is perceptible. By using the proposed mesh stiffness of meshing gears, for the system with numbers of odd and even equally and unequally spaced planets, natural frequencies and vibration modes are validated with a high accuracy.

As an effective indication signal, vibration tactile has been widely studied. However, there is still a lack of comparative studies on the use of tactile interaction perception of both static vibration and dynamic vibration as direction indication signals for walking-assistance navigation products for the limited vision. Limited vision people have to perceive the travel environment through nonvisual senses. Besides, vibration and touch can reduce cognitive pressure in complex environments compared with auditory. This study aimed to compare the comprehensive interactive perception of direction indication by both static vibration and dynamic vibration in walking-assistance navigation products for limited vision people. In the tactile interaction perception experiment of static vibration and dynamic vibration, twenty-four participants were involved in the experiment. We measured the direction reaction time, the correct number of direction perceptions, and asked participants to evaluate the degree of perception and perceived comfort in each mode. It can be seen from the results that compared with the dynamic vibration, the static vibration had a higher correct perception numbers (F = 10.394, P = 0.006) and a shorter reaction time (F = 5.276, P = 0.038). And participants’ perception degree (F = 21.221, P < 0.001) and comfort degree (F = 47.692, P < 0.001) in static mode were higher than those in dynamic mode. In conclusion, the static vibration is superior to the dynamic vibration in terms of the comprehensive perception of direction indication. The static vibrotactile interactive perception is preferred as a direct indication signal in the walking-assistance navigation products for the limited vision.

In order to evaluate the impacts of parameter uncertainty and nonparametric uncertainty on the natural characteristics of a dual-rotor system, a nonparametric probabilistic method based on random matrix theory is proposed. In this paper, a nonparametric Riccati whole transfer model is derived based on the maximum entropy principle and the random matrix theory. It is used to model a dual-rotor system with nonparametric uncertainty, as well as to calculate the natural characteristics of the system. Furthermore, the impacts of parameter uncertainty and nonparametric uncertainty on the natural characteristics at the intermediate support element and at the disk-shaft element are discussed using numerical simulations, and the results are compared with related references. The results show that at the same level of uncertainties, the effect of nonparametric uncertainty is often more significant than that of parameter uncertainty. The effects of uncertainties also increase with the level of uncertainties. The results of this paper provide a theoretical basis for the design of uncertain dual-rotor and multi-rotor systems. [ABSTRACT FROM AUTHOR]